docs: def stat_by_index(self, stat, level=0):
          """
          Compute the desired statistic for each uniue index values (across levels, if multi-index)
  
          Parameters
          ----------
          stat : string
              Statistic to be computed: sum, mean, median, stdev, max, min, count
  
          level : list of ints, optional, default=0
              Specifies the levels of the multi-index to use when determining unique index values.
              If only a single level is desired, can be an int.
          """
          from numpy import sum, min, max
  
          STATS = {
              'sum': sum,
              'mean': mean,
              'median': median,
              'stdev': std,
              'max': max,
              'min': min,
              'count': size
          }
          func = STATS[stat.lower()]
          return self.aggregate_by_index(level=level, function=func)